Method of operating vapor jet vacuum pumps



Jan. 3, 1939. P. SCHLUMBOHM METHOD OF OPERATING VAPOR JET VACUUM PUMPS Original Filed Feb. 27, 1956 Patented Jan. 3, 1939 PATENT OFFICE METHOD or ornas'rmc varon. nz'r vacuum s PUMP , Peter Schiumbohm, York, N. Y.

Befiled ior abandoned application Serial No. 65,959, February 27, 1938. This application December 13, 1937, Serial No. 179,457. I In Germany May 4, 1933 3 Claims.

This application is a reflle o! my former application, Ser. No. 65,959, filed Feb. 27, 1936, and later abandoned.

The present invention relates to a method of improving the vacuum efiect of ejector pumps. In such ejector pumps the vapor of substances with low vapor pressure, like mercury, oil or water, leaves a nozzle and enters into a diffusor. The free space between the edge 01 the nozzle and the wall of the diffuser forms an annular channel and is called the suction channel. The nozzle is inserted into the Jsuction chamber which is in open connection with the space to be evacuated. The dimensions is of the suction channel influence greatly the degree oi vacuum obtainable by a certain vapor; but even at the optimum'conditions chosen for the suction channel, there is an "end vacuum, -i. e. a limit of a degree of vacuum obtainable by so that vapor. The end vacuum reachable with mercury and oil is satisfactory ior all practical purposes: when using water steam, however,

it is diflicult to reach in a single stage ejector a vacuum below. 2 mm. With very complicated as arrangements, e. g. tour stage ejectors with condensation between the single stages, and requiring high steam pressures, it was possible to reach 0.4 mm. Hg vacuum. By my present invention it is possible to reach :0 in a single stage and with the extremely low steam pressure of less than one atmosphere abs. a vacuum of 0.1 mm. Hg, while using water steam as propellant vapor.

The invention relates further to the construc- 35 tion of an apparatus, in which the new method may be applied.

The invention is illustrated in the accom-' panying drawing, which may be considered as diagrammatic so as to include other construc- 40 tions.

Fig. 1 is asectional view illustrating the operation of an ejector.

Fig. 2 shows, mainly in cross section and partly in view, an elector pump which actually has been as built all in glass and the drawing is based on the constructional drawing or the working model,

except for the dimensions oi jetfdifl r, water Jet pump and liquid columns. v

The invention was the consequence oi a 60 theoretical deliberation concerning the mechanism of the vacuum effect of a steam jet, and

' it was a great satisfaction tosee the theoretical conclusion confirmed by the very first experimental attempt made to prove it. The conclull sionwas (seems. i) that the endvacuumwould be reached at the moment when part of the steam 2, leaving the nozzle I and entering into the diffuser 5, would diffuse back into the suction channel 3 and form therea vapor cushion of steam, and that such a stationary vapor cushion 5 would make it impossible for an air molecule to diffuse from the suction chamber 4- into the suction channel 3 to be carried away by the steam 2 into the difi'usor 5. The invention now is: to absorb this cushion of vapor chemically. m

When this is done, the end vacuum is improved greatly, in the case 01 water vapor to 0.1 mm. Hg. Following the invention, the absorption of the vapor cushion in the suction channel is effected by a chemical absorbing means-specific for the kind of vapor appliedwhich enters continuously into the suction channel 3 Csee Fig. 2). In the case of water steam as propellant vapor, the chemical absorbing means may be constituted by hygroscopic. fluids like sulphuri acid, potassium hydroxideor sodium hydr desolutions or the like. In-Fig. 2 the sulphuric acid enters from atmospheric pressure through tube l3 into a distributor I4 arranged within the vacuum space 22 and trickles through holes i6 25 into the suction chamber 4 of the steam nozzle I; as indicated by the tail-end arrows the sulphuric acid flows into the suction channel 3, then into the difiusor 5, then into a liquid trap I2,

from which it may be eliminated by a water jet a pump 1, leaving through the off-water tube 23.

The air to be pumped by the steam jet l is characterized by feather-end arrows, entering the vacuum space 22 through a suction tube It! and leaving space 22 through suction chamber 4, suction channel 3, difiusor 5, pre-vacuum space 7 2|, air-suction tube 80f the water jet pump 1,

and finally through the'ofl-water tube 23.

When checking up the improvements obtained by introducing chemical absorbing means into 40 the suction channel 3, I found that such absorbing means were also eifective in the difiusor 5, and I conceived the idea to absorb the total amount of steam entering into the difiusor 5 in-' stead of condensing the vapor as usual in steam ejectors'. This part of the invention stands on i. its own merit, independent of the step of introducing absorbing means into the suction channel, and may prove to be 01 general usefulness. However, it is 0! special value in the present case in connection with the other part of the invention as mentioned above, as it increases the efliciency oi the steam ejector itself, independent of the above mentioned new vacuum effect. It was found that chemical absorbing means for u a the vacuum eflect are introduced through the suction channel.

As illustrated in Fig. 2 the body of the pump, which comprises the pre-vacuum water jet pump 1, the high-vacuum pump I, 3, 4, 5 and the suction tube I9 is constituted by an outer casing 20, the inside space of which is subdivided into th pre-vacuum space 2|, in which a 12 mm.-15 mm.

pressure is created and maintained by the water jet pump], and into the high-vacuum space 22,

in which the steam ejector creates and maintains a vacuum of e. g. 0,1 mm. The two pressure spaces 2| and 22 are separated from each other by a, liquid trap in the communicating annular spaces l1 and I8. This arrangement makes it possible to introduce absorbing means into the pre-vacuum space 2| for the absorption of the steam without using the suction channel for introducing them. As shown in the Fig. 2 the distributor M 'for the absorbing liquid has, holes I5 through which the sulphuric acid may trickle over the outer wall of the water cooled doublewalled body H), which is arranged vertically, being with its upper part in the high-vacuum -zone 22 and with its lower part in the pre-vacuum zone 2|. "bn its way over the outer wall of body Hi the absorbing liquid will in t e high- I vacuum-zone 22 be useful for absorbi vapors coming from an evaporator through tube IS, a process as described in my U. S. A. Patent No.

1,894,893. Passing through the liquid trap n,'

|8-part l8 being built as an overflowthe absorbing liquid, rinsing over the outer wall of body I0, enters into the prevacuum zone 2| and absorbs the vapor which comes from the difiusor 5, as indicated by the feather-end arrows. The

, absorbing liquid, diluted by the absorbed vapor,

drips to the bottom of casing 20, where it joins the absorbing liquid, which was introduced into the suction channel, and from where it flows through liquid trap l2 into the water jet pump 1' and its oiT-water tube 23. The cooling water for cooling body l0 enters through tube 9 and then serves to run the water jet pump 7. Steam .fo1 the nozzle enters through tube 6.

I found that a steam pressure as low as about 190 mm. Hg, corresponding to about 65 C. hot water, is suflicient to obtain- 0.1 mm. vacuum under the conditions as described above. Such a pressure is only a fractionof the pressures now applied in steam ejector vacuum pumps, and this feature of the inventions involves a great economy.

The economy of the apparatus as shown in the drawing may be improved by withdrawing the diluted absorbing means from container |2 for reconcentration purposes, instead of letting the diluted acid flow into a water jet pump. For

small capacities, however, it does not pay to recover the absorbing liquid, and then the further dilution by the oil-water or the water jet pump is quite convenient .for carrying the sulphuric acid or the like away into the sewer system in a highly diluted form.

The apparatus as shown in Fig. 2 combines the features 01' the pr s nt invention with-thereatures of my U. 8. Patent 1,894,893. In saidpatent, however, a mechanical high vacuum pump of the type of a rotary oil pump or of the type of a. mercury vapor pump was required to withdraw the air from the high-vacuum absorben' By the present invention allfunctions are achieved by a two chemicals only: water and the absorbing liquid. If the new. high-vacuum steam ejector oi the present invention is combined with a highvacuum absorber for water vapors as described in U. S. Patent 1,894,893, said combination being shown in Fig. 2 01! the present patent application, then the capacity of the steam eje'ctori can be chosen very small, as only small amounts of air are to be pumped. The main pumping job isdone in that case by the absorbing liquid which trickles through the holes l5 over the outer wall of the water cooled body l0 within the high-vacuum space 22, where it is exposed to water vapors coming from an evaporator portance of the present invention. At such low has a huge spe-' evaporator temperatures water cific vapor volume (at 0 C. 18 gr. of water evolve about 3.000 litr. of vapor) and the great flow speed of such water vapors as required for an emcient pumpingcan only be obtained if the absorber is free of air.

Having now described my invention and indicated by way of example the manner in which it is to be performed,

What I claim is:

1. In the method oi. operating a steam vapor jet vacuum pump the step of introducing continuously into the pump a fluid adapted to absorb the propellant vapor applied, the step 'of absorbing propellant vaporby means of said absorbing fluid and the step of withdrawing from the .pump said absorbing fluid diluted by absorbed propellant vapor.

2. In the method as claimed in claim 1, the

step of introducing said absorbing fluid into the said absorbing fluid into the pre-vacuum zone of the vapor jet to absorb the propellant vapor which leaves the diifusor of the vapor jet.

" PETER SCHLUMBOHM. 

